The present invention relates to cases with flat lugs for medium power semi-conductor components.
Among the different techniques for mounting power semi-conductor cases on apparatus in which they are used, there is at present a growing demand for cases with flat tags, particularly, for cases with Faston lugs, i.e. lugs each complying with pre-established standards in so far as their linear dimensions and thicknesses are concerned, and allowing rapid wiring up by means of female connectors fitting on to said lugs. But other presentations of cases with flat lugs are demanded by users for satisfying different needs for mounting in particular apparatus, more especially for series or parallel mounting.
The present invention provides a process for manufacturing a case so that, in the last manufacturing step only, a choice may be made between different modes of presentation and of conforming the connecting lugs depending on the desiderata of a particular user.
Before describing the present invention, and so as to better bring out the interest and advantages thereof, there will be described with reference to FIGS. 1 and 2 an example of a case with Faston lugs constructed with the current technique.
FIG. 1 shows in perspective a conventional flat-lug case during an intermediate manufacturing step before being sealed in a plastic material. The case comprises a base 1 made from a good heat conducting metal, for example copper coated with a metal layer adapted to facilitate soldering. This base may comprise bores 2 more particularly for providing simple fixing thereof against a heat-sink. On the base there is disposed a plate 4 of an electrically insulating material and also as good a heat conductor as possible, for example alumina metallized on both its main faces. On the electrically insulating plate 4 there is disposed a plate 5 made from a very good heat conducting material which will generally be electrically conducting, for example a copper plate coated with a material adapted to facilitate brazing. The purpose of this plate is to distribute as well as possible the heat flux to be evacuated through base 1 before it passes through plate 4. On this plate 5 are disposed one or more semi-conductor components 6 and 7 in the form of a naked chip with metal coated faces. By way of example, these components may be transistors whose face in contact with the conducting plate 5 corresponds to the collector and whose upper face comprises a base terminal and an emitter terminal. The collector terminals are then interconnected by means of metal plate 5. Lateral parts of the electrically insulating plate 4 comprise metal layers separated from the main upper metallization of this plate. On these separate metallizations are brazed the proximal part of small metal plates 10 to 13 whose distal parts are shaped in accordance with the specific Faston lug standards. Chosen terminals of each of the semi-conductor components 6 and 7 are connected by connecting wires 14 to a zone at the proximal end of the flat lugs or tags 10 to 13. FIG. 1 shows by way of example the internal wiring of a Darlington circuit in which component 6 is the driver transistor, component 7 is the output transistor, connection 11 is the base of the driver, connection 12 is the base of the output stage, connection 10 is the emitter and connection 13 is the collector.
In a subsequent manufacturing step, the result of which is illustrated in FIG. 2, lugs 10 to 13 are bent upwards orthogonally to the surface of the base and the whole is molded in a block of plastic material, for example an epoxy resin 16. The operation may be effected either by transfer molding by disposing the case or rather a series of cases in a mold of chosen shape, or else, as is more particularly shown in FIG. 2, by using a lost mold technique, i.e. by disposing a cap having an opening 17 on the base then flowing resin or other plastic material into this cap.
The case described above with reference to FIGS. 1 and 2 gives satisfactory results as conventional Faston lug case. Nevertheless, its drawback is that, after molding of the sealing plastic material, the connecting lugs cannot be simply altered or disposed in another configuration so that the user has at his disposal connecting lugs in another configuration for adapting to a particular wiring method.